UK parliament has been recalled early and will meet on Thursday to discuss any future action and to vote on the UK’s response to the attack.

David Cameron’s spokesman said that the prime minister believes the chemical weapons attack, in which hundreds of people are reported to have been killed, is “absolutely abhorrent” and that the international community must respond.

He went on to say that Britain is considering a “proportionate response”, and that it is reasonable to assume that Britain’s armed forces are making contingency plans on how to respond.

No decisions on military action have been taken, and the spokesman said Britain will wait for evidence being gathered by a team of United Nations inspectors in the area, before making any decision.

“Any decision taken will be taken under a strict international framework,” he said, adding: “In terms of end-game, this is about looking at how we deter the use of chemical weapons because this is something that is completely abhorrent and against all international law.

“This is about deterring the use of chemical weapons.”

MPs were due to return to parliament from summer recess on 2 September.

UN inspections

In a press conference, Syrian Foreign Minister Walid Moualem said that the second day of a United Nations (UN) inspection team’s work had been postponed to Wednesday due to disagreements among the rebels over security arrangements.

Inspectors are trying to confirm if chemical weapons were used – not who may have used them – but there are fears that the delay in their inspection will make it difficult to determine.

This is about looking at how we deter the use of chemical weapons because this is something that is completely abhorrent Downing Street spokesman

During the press conference, Walid Moualem also said that Syria “utterly and completely” rejected accusations made by the US that the Syrian government was behind the chemical attack, and said Syria will defend itself by “all means available” against any foreign strikes: “The (government’s) military effort will not stop around Damascus.

“If the purpose (of foreign strikes) is to limit the victories of our armed forces, they will not be successful.”

“President (Barack) Obama believes there must be accountability for those who would use the world’s most heinous weapons against the world’s most vulnerable people,” he said. “The indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity. By any standard, it is inexcusable. And despite the excuses and equivocations that some have manufactured, it is undeniable.”

Military chiefs from the US and its European and Middle Eastern allies have met in Jordan for what could be a council of war, should they decide to punish President Assad. However Moscow – a key regime ally which supplies arms to Syria – has backed Syrian claims that video footage of victims could be opposition propaganda.

In comments to a Russian newspaper, the Syrian president warned the US against any military intervention and denied government forces were responsible for any chemical weapons attack.